As a method for connecting semiconductor chips to a circuit board such as an interposer, conventionally, wire-bonding connection and flip chip connection have been widely used. Recently, however, a method for mounting the semiconductor chips respectively on a plurality of interposers, and connecting these interposers with each other has been proposed, in order to increase the capacity of a memory.
In this case, not only the connection between the semiconductor chips and the interposer, but also the connection between the interposers is required. The method therefor includes a method of using a metal pin as described in Japanese Patent Laid Open No. 2002-76240, a method of using a bonding wire, and a method of using a solder.
The connection using the bonding wire can realize highly accurate connection, but on the other hand, operation time increases in proportion to the number of terminals, since it is necessary to connect the terminals to be connected one by one. Further, since the connection using the bonding wire is a planar connection, it is essentially difficult to decrease the size of the whole semiconductor device. Thus, when a plurality of interposers are connected to each other by using the bonding wire, there are problems in that the operation time is prolonged and the size of the whole semiconductor device increases.
On the other hand, the method of using the solder has an advantage in that the operation time is relatively short, but if coefficients of thermal expansion of the interposers differ largely from each other because of the copper distribution, misregistration occurs due to heating at the time of joining, and hence, it is difficult to apply this method to a semiconductor device having terminals with a narrow pitch. Further, the solder may remelt in a reflow process in which the stacked semiconductor device is mounted on a module board or a motherboard, and as a result, adjacent terminals may be short-circuited, thereby damaging reliability.
The above problems occur not only when a plurality of interposers having semiconductor chips mounted thereon are connected to each other, but also, for example, when a flexible sub-interposer having semiconductor chips mounted thereon is connected to a rigid main interposer.
On the other hand, since the connection using the bonding wire is a planar connection, even if the circuit boards such as the interposers are opaque or semitransparent, this does not cause a problem at the time of connection.
However, when the circuit boards such as the interposers are connected by superposition, if the circuit boards are opaque or semitransparent, visual recognition or image recognition of the terminals is not possible, or becomes very difficult, thereby causing a problem in that accurate connection becomes difficult. Such a problem does not occur when the terminals are protruded from the circuit board, but if the terminals are not protruded from the circuit board, and formed on the circuit board, it becomes a major problem.